In many integrated circuits it is common to isolate a signal source from a load by buffering. One advantage of buffering is that it can be used to prevent a large load from interfering with the operation of the signal source. Thus a well-designed buffer will provide a much smaller load impedance to the signal source than the load being driven by the buffer.
In some circumstances the buffer is required not only to isolate the load but also to translate the signal output by the signal source from one voltage level to another. For example in modern complementary metal oxide semiconductor (CMOS) integrated circuit fabrication processes, it is common to have multiple gate oxide thicknesses to accommodate both high-voltage and low-voltage transistors. The thicker gate oxide of the high voltage transistors make them able to withstand higher gate voltages without causing harmful stress to their gate oxide. Thus they may be used in higher voltage circuits. For example, a digital input buffer may use high-voltage transistors to receive an external signal that varies between 0 and 3.0 volts.
Sometimes an external signal source or a circuit using high voltage transistors produces a time-varying (AC) signal with a relatively large peak-to-peak voltage. Since this signal must be subsequently processed in circuitry using low-voltage transistors, the buffer must also scale the peak-to-peak voltage so that it does not damage the low-voltage transistors. Some such circuits are known for radio frequency (RF) applications, and as used herein, a radio frequency signal means an electrical signal conveying useful information and having a frequency from about 3 kilohertz (kHz) to thousands of gigahertz (GHz), regardless of the medium through which such signal is conveyed. Thus an RF signal may be transmitted through air, free space, coaxial cable, fiber optic cable, etc.
However modern CMOS processes have made more RF processing possible on-chip. At the same time, new buffers suitable for isolating loads from signal sources and translating signals from one voltage level to another are needed.